Validation of the Portuguese version of the Movement Disorder Society non-motor rating scale (MDS-NMS) in Parkinson's disease

Background: The Movement Disorder Society Non-Motor Rating Scale (MDS-NMS) serves as a comprehensive clinical assessment tool for non-motor symptoms in Parkinson's disease (PD) Objectives: This study aims to validate the Portuguese version of the MDS-NMS, addressing the critical need for culturally adapted rating scales in Portuguese-speaking populations. Methods: This multicenter, cross-sectional study engaged native Portuguese-speaking PD patients from 16 Movement Disorders Centers across Portugal and Brazil. We conducted a meticulous translation process into Portuguese, including forward-backward translation and cognitive pretesting. Confirmatory factor analysis (CFA) and exploratory factor analysis (EFA) were conducted to evaluate the psychometric properties and structural validity of the Portuguese version in comparison to the original English version. Tertiary analyses assessed the acceptability and reliability of domain scores within the cohort. Results: The scale was administered to 386 PD Portuguese-speaking patients. CFA, conducted with a final sample of 303 participants, confirmed that the Portuguese version maintained a factor structure consistent with the English original, with Comparative Fit Index (CFI) values meeting or exceeding the 0.90 threshold across all subscales. High CFI values in domains such as Depression, Psychosis, and Cognition underscored the robustness of the translation. EFA revealed generally strong item-factor relationships, although domains like Gastrointestinal and Non-Motor Fluctuations exhibited more complex structures. Reliability analyses demonstrated strong internal consistency, with Cronbach's alpha ranging from 0.50 to 0.86 across domains, further corroborated by McDonald's omega and Greatest Lower Bound values. Conclusions: The Portuguese version of the MDS-NMS demonstrates psychometric properties and structural validity that closely aligns with the original version.